Make ecp_get_type public

The ecp_get_type function comes handy in higher level modules and tests
as well. It is not inline anymore, to enable alternative implementations
to implement it for themselves.
diff --git a/tests/suites/test_suite_ecp.function b/tests/suites/test_suite_ecp.function
index f1f96a1..ba271b1 100644
--- a/tests/suites/test_suite_ecp.function
+++ b/tests/suites/test_suite_ecp.function
@@ -760,12 +760,7 @@
     if( ret == 0 )
     {
         TEST_ASSERT( mbedtls_mpi_cmp_mpi( &P.X, &X ) == 0 );
-        /*
-         * At the time of writing, the following condition is equivalent with
-         * if( ecp_get_type( grp ) == ECP_TYPE_MONTGOMERY )
-         * but has the advantage of not using internal symbols.
-         */
-        if( grp.G.Y.p == NULL )
+        if( mbedtls_ecp_get_type( &grp ) == MBEDTLS_ECP_TYPE_MONTGOMERY )
         {
             TEST_ASSERT( mbedtls_mpi_cmp_int( &Y, 0 ) == 0 );
             TEST_ASSERT( P.Y.p == NULL );